Some breastfeeding benefits questioned by US study

SOME of the common claims about the long-term benefits of breastfeeding – that it can boost IQ and protect against health conditions in later life – have been cast into doubt by a new study.

Unsurprisingly, considering how contentious the issue of whether women should breastfeed is, the work has already been criticised. So how much can studies tell us about breastfeeding’s possible benefits?

Comparisons of babies born into different families have suggested that breastfed babies are less likely than bottle-fed babies to become obese or to develop asthma, diabetes and childhood cancers. Breastfed children have also been found to score 3 to 6 IQ points higher on average.

But other factors could be at play. For example, in many countries, breastfeeding is more common in wealthier families. To take such differences between families into account, Cynthia Colen and David Ramey of Ohio State University in Columbus looked at siblings in 665 families in the US where one child was breastfed and another bottle-fed. They found that breastfeeding gave no benefits in a range of measures including obesity, BMI, asthma and academic achievement (Social Science & Medicine, doi.org/rqq). Colen and Ramey claim that the past findings reflect differences between families such as income, access to healthcare or the home environment. But others say that the design of Colen and Ramey’s study is also flawed.

Ideally, a randomised controlled trial would be used to tease out the influence of social and economic factors, but it would be unethical because it would involve telling groups of mothers how to feed their babies. So researchers have had to find other ways to remove social influences.

This fits with a study of 14,500 babies born in the UK in the 1990s. Breastfeeding was linked with better health at age 7 and 9 and higher IQ at 4. However, when the results were compared with data from Brazil, where breastfeeding isn’t linked to socio-economic status, only the IQ result held.

Colen and Ramey’s work found no effect on IQ, but Kramer questions their use of siblings because the decision to breastfeed one child and not the other isn’t random.

Mary Renfrew at the University of Dundee, UK, agrees that the study was poorly designed. For instance, babies fed a mix of breast and formula milk would still have been classed as breastfed. However, Joan Wolf at the Texas A&M University in College Station says the results fit a pattern&colon; the more studies control for variables, the smaller the long-term impact of breastfeeding seems to be.

Either way, breastfeeding is best, because of short-term protection against infections, says Colen. But, in the long-term, less effort should be put into promoting it, she says, and more into other ways to help poorer households.

This article appeared in print under the headline “How can we test if breast is best?”